Imported "rxjs/add/observable/throw" to enable Observable.throw

So that we don't get "throw" is undefined when an error occurs.

Author: willemodendaal

src/directLine.ts

@@ -22,6 +22,7 @@ import 'rxjs/add/observable/empty';
 import 'rxjs/add/observable/from';
 import 'rxjs/add/observable/interval';
 import 'rxjs/add/observable/of';
+import 'rxjs/add/observable/throw';
 
 // Direct Line 3.0 types